1. Field of the Invention
The present invention relates to a process of preparing a spherical powder of titanium nitride or titanium carbonitride, optionally containing a metal of the IVa, Va and VIa groups of the periodic table, and a novel powder of this type.
2. Description of the Prior Art
Titanium nitride, titanium carbonitride and mixed titanium carbonitrides are used primarily in the manufacture of cermet cutting materials, shaping tools and wear-resistant parts. Cermets are materials in which a ceramic is heat-bonded to a metal in which it is embedded. In addition to the indicated nitrides, many cermets also contain carbides of metals of the Va and VIa groups of the periodic table. The most desirable properties for specific uses, such as machining of steel, are obtained by suitably combining these hard materials and varying the grain size and shape of the hard material particles. European patent No. 512,967, for example, discloses that excellent properties for forming and milling may be obtained with hard titanium carbonitrides of different grain sizes.
Various processes for preparing titanium nitride, titanium carbonitride and mixed titanium carbonitrides are known. At present, the prevailing process of preparing titanium carbonitride, which optionally may contain other substances, comprises annealing a reaction mixture of titanium carbide optionally containing other carbides and/or metals with carbon and titanium nitride in a nitrogen atmosphere at a temperature of about 1500.degree. C. In another known process, the selected metal powders are reacted with nitrogen, with the optional addition of carbon. In a reaction described by E. Friedrich and L. Sittig in 1925, titanium nitride containing carbon is obtained by reacting titanium oxide with carbon and nitrogen. To obtain a product containing between 0.3-1%, by weight, of oxygen, temperatures around 2000.degree. C. are required. Since the high reaction temperature causes the product to be sintered together, it must be milled in a very expensive comminution stage to obtain the desired grain size. At any rate, the resultant product is a powder of a wide grain spectrum and a splintered polygonal shape.
Austrian patent No. 394,188 which corresponds to U.S. Pat. No. 5,147,831, describes a process of preparing a fine-grained titanium nitride or carbonitride powder on the basis of the oxide, which has spherical grains and a narrow grain spectrum. However, it has not been possible to prepare with this process a coarse-grained powder of spherical shape and a narrow grain spectrum.